Aux battery disconnect

[Mguy]

The depth of discharge/longevity discussion is off the mark.

The 50% discharge general recommendation, generally accepted, represents a practical compromise for deep discharge utility vs. lifetime cycles when using AGM "deep cycle" batteries.

However, 99% of Jeep owners have no use for, and typically don't have, such batteries. Deep cyclers are generally found in RVs, boats, and solar systems. The main battery in Jeeps is for starting, requiring no deep discharging, and so should rarely ever reach any discharge even approaching 50%.

Perhaps those who regularly winch, use engine-off refrigeration, or habitually leave the lights on and need jumps in the morning should be interested in deep cycle battery characteristics. The other Jeep owners need only be concerned with keeping their main battery fully charged.

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[AndySpill]

@THAW, once again you've gone into "Sheldon" (from Big Bang Theory) mode, so eager to correct the science that you've lost your way on the practical aspects at play here.

Yes, if you want to maximize the total amp hours of a stand alone AGM battery an argument could be made for deeper than 50% discharge because it involves less recharge cycles to bring the battery back to full capacity than are necessary if you take the battery to only 50%.

The argument here is that even though bringing the battery down to 20% will reduce the overall number of recharge cycles you have when compared to taking the battery down to only 50%, that these reduced number of charge cycles are enough offset by making each of those lessened amount of recharge cycle more productive (an 80% versus 50% refilling process.)

Great. Go take your stand alone AGM batteries down to 80% with my blessing.

But the Aux battery in this scenario was one likely to be reconnected to the main battery, in which case the more charge cycles we can get out of it the longer it lasts and hopefully doesn't take the main battery out with it when it dies...that even if it doesn't, running dual AGM battery best practices finds it indicated to replace both batteries when either or both batteries age out.

We are trying to maximize the lifespan of our horse (Aux battery) here, more than the number of miles it walks in its life.

 

[THAW]

However, 99% of Jeep owners have no use for, and typically don't have, such batteries. Deep cyclers are generally found in RVs, boats, and solar systems. The main battery in Jeeps is for starting, requiring no deep discharging, and so should rarely ever reach any discharge even approaching 50%.

Ever heard of ESS? Supporting vehicle electronics during auto stops is the main reason most vehicles now have factory AGMs.

 

[Mguy]

Ever heard of ESS? Supporting vehicle electronics during auto stops is the main reason most vehicles now have factory AGMs.

JL's also have an Accessory position on the start button, so what?

If you think ESS, or the aux battery itself, constitute, or are suitable for, deep cycling, you're in deep shit.

Sorry, I mean your batteries are in deep shit.

 

[THAW]

JL's also have an Accessory position on the start button, so what?

If you think ESS, or the aux battery itself, constitute, or are suitable for, deep cycling, you're in deep shit.

Sorry, I mean your batteries are in deep shit.

Jeep engineers specifically designed the JL ESS system to allow cycling the CR[an]K battery down to 65% SoC. Apparently you've never commuted in stop-and-go traffic, but it's a common, real-world use case (in fact, it's an original, primary justification for development of auto stop/start systems).

 

[Mguy]

Jeep engineers specifically designed the JL ESS system to allow cycling the CR[an]K battery down to 65% SoC . . . .

Thanks, I really appreciate you helping to prove the point!

Too many JL owners, with typical ESS use, unknowingly place an unreasonable burden on their battery charging system. And again, too often it doesn't even matter that they don't have an aux battery hooked up. Helping those hapless owners is what this forum should be about.

But wait, I forgot, you're a JL electrical expert. With your valuable JScan data you found a way to live with either regular external charging or regular battery swapping. Fine, as is often said on this forum, "you do you."

Best of luck Lucy.

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